Electrophotographic multicolor copy process employing solubilizable dyes

ABSTRACT

THIS INVENTION IS ADDRESSED TO AN ELECTROPHOTOGRAPHIC COPY PROCESS FOR THE PRODUCTION OF TRUE COLOR COPIES IN WHICH AT LEAST TWO RECEPTOR SHEETS, EACH OF WHICH IS PROVIDED WITH A BINDER, A PHOTOCONDUCTOR, A SENSITIZING COMPONENT WHICH ENSITIZES THE PHOTOCONDUCTOR TO AT LEAST A PORTION OF THE SPECTRUM OF VISIBLE LIGHT AND A DISPERSED DYE OF A DIFFERENT COLOR ON EACH RECEPTOR, ARE SEPARATELY IVEN AN ELECTROSTATIC CHARGE AND EXPOSED TO AN ORIGINAL SUCH AS A MULTI-COLOR ORIGINAL, AND THE EXPOSED RECEPTOR SHEETS ARE THEREAFTER DEVELOPED WITH A DEVELOPER COMPOSITION CONTAINING A TONER IN THE FORM OF A MATERIAL WHICH, IN RESPONSE TO ACTIVATION, SERVES AS A SOLVENT FOR THE DISPERSED DYE TO EFFECT TRANSFER OF THE DYE COLOR FROM THE UNDERLYING PORTIONS OF EACH COATING TO A COPY SHEET PRESSED INTO SURFACE CONTACT WITH EACH RECEPTOR.

Apn] 17, 1973 .N. CHAPIN ET AL 3,728,112

ELECTROPHO RAPHIC MULTICOLOR COPY PROCESS EMPLOYING SOLUBILIZABLE DYES Filed Dec. 1; 1970 20 FIG. 1 :10

FIG. 5 I v 22 F! G. 4 if FIG. 5

CIH Q" FIG, 6 0

.65 W. Giza Din wwwaw azzys Robert Jreeal United States Patent 3,728,112 ELECTROPHOTOGRAPHIC MULTICOLOR COPY PROCESS EMPLOYING SOLUBILIZABLE DYES Leo N. Chapin, Des Plaines, and Robert Freed, Lincolnwood, Ill., assignors to A. B. Dick Company, Niles, Ill. Filed Dec. 1, 1970, Ser. No. 94,125 Int. Cl. G03g 9/02, 13/08, 13/14 US. Cl. 961.2 21 Claims ABSTRACT OF DISCLOSURE This invention is addressed to an electrophotographic copy process for the production of true color copies in which at least two receptor sheets, each of which is provided with a binder, a photoconductor, a sensitizing component which sensitizes the photoconductor to at least a portion of the spectrum of visible light and a dispersed dye of a different color on each receptor, are separately given an electrostatic charge and exposed to an original such as a multi-color original, and the exposed receptor sheets are thereafter developed with a developer composition containing a toner in the form of a material which, in response to activation, serves as a solvent for the dispersed dye to effect transfer of the dye color from the underlying portions of each coating to a copy sheet pressed into surface contact with each receptor.

This invention relates to a new electrophotographic copy process for the production of true color copies from a multi-color original.

A well-known electrophotographic copy process, generally referred to as the Xerox process, is described in US. Patent No. 2,297,691 to Carlson, in which a receptor having a photoconductive coating or layer is given a blanket electrostatic charge under subdued light or in the dark, such as by ion transfer from a corona discharge. Thereafter, the photoconductive coating or layer is exposed to light modified by an image, such as by projection of a photographic image onto the photoconductive layer. The illuminated areas of the photoconductive layer, corresponding to the non-imaged areas of the original, are rendered conductive whereby the illuminated areas are discharged to leave a latent electrostatic image on the photoconductive coating or layer corresponding to the imaged portions of the original.

The resulting latent electrostatic image can then be developed, as by dusting with an electroscopic powder, such as a pigmented resinous powder carrying an opposite electrostatic charge whereby the pigmented powder is electrostatically attracted to the oppositely charged latent electrostatic image, as is described in US. Patent Nos. 2,618,551, 2,788,288 or 2,940,934. Development of the latent electrostatic image can also be achieved by use of a liquid developing composition of the type described in US. Patents Nos. 2,877,133, 2,891,911 and 2,290,674. In either case, the powder or pigment of the powder or liquid developer, often referred to as toner, adheres to the electrostatically charged latent image.

The resulting developed image can be used in a variety of ways. For example, it can be fixed to form the developed image directly on the photoconductive coating or layer on the receptor, or it can be transferred from the photoconductive coating on the receptor to a copy sheet to be fixed on the copy sheet.

Electrostatic copy techniques of the type described above have been adapted for use in the production of multi-color copy, most frequently by the use of a number of developer compositions, each of which contains a toner having a different color. Thus, each color must be formed by developing the latent electrostatic image formed on the exposed receptor with a different toner,

ice

thereby resulting in a very cumbersome operation in the development of multi-color images.

It is accordingly an object of the present invention to provide a new and improved electrophotographic copy process for the production of true color copies which overcomes the aforementioned disadvantages.

It is a more specific object of the present invention to provide a new and improved electrophotographic copy process for the production of true color copies in which the color of the copy is contained in the photoconductive layer whereby it is unnecessary to employ a different toner for each color to be developed.

It is yet a further object of the invention to provide a new and improved true color copy process of electrophotographic technique in which the color of the copy is independent of the toner employed in the development of the latent electrostatic image.

These and other objects and advantages of this invention will appear more fully hereinafter, and, for purposes of illustration, but not of limitation, an embodiment of the invention is shown in the accompanying drawings in which:

FIG. 1 is a sectional view of one of the two or more receptors embodying the concepts of the invention;

FIG. 2 is a perspective view of a first receptor of the type shown in FIG. 1 after exposure in accordance with the practice of the invention;

FIG. 3 is a perspective view of a second receptor of the type shown in FIG. 1 after exposure in accordance with the practice of this invention;

FIG. 4 is a perspective view of a third receptor of the type shown in FIG. 1 after exposure in accordance with the practice of the present invention;

FIG. 5 is a schematic sectional view of one of the receptors of FIGS. 2 to 4 after development of the latest electrostatic image;

FIG. 6 is a schematic illustration of this transfer of the image from one of the developed receptors of FIGS. 2 to 4 to a copy sheet; and.

FIG. 7 is a top plan view of the multi-color copy produced by the transfer of the developed image from the receptors of FIGS. 2 to 4.

The concepts of this invention reside in a new and improved electrophotographic copy process for the production of true color copy in which at least two, and preferably three or more receptors, each of which is provided with a photoconductive coating formulated to contain (1) a resinous binder, (2) a photoconductor, (3) a sensitizing component which sensitizes the photoconductor to at least a portion of the spectrum of visible light and (4) a dispersed dye of a different color on each receptor, are separately given an electrostatic charge and successively exposed to an original such as a multi-color original. Thereafter, each of the receptor sheets having a latent electrostatic image thereon is developed with a developer composition containing a toner in the form of a material which, in response to activation as by heat, solvent, vapors or the like, serves as a solvent for the dispersed dye (4) in the photoconductive coating to effect transfer of the dye color from the underlying portions of each coating to a copy sheet pressed into surface contact with each receptor.

In accordance with one embodiment of the invention, the photoconductive coating on each receptor contains a sensitizing component in the form of a sensitizing dye which sensitizes the photoconductor to light of a selected wave length within the spectrum of visible light while reflecting wave lengths outside that wave length, whereby the total of all the receptors provides sensitivity which substantially covers the entire spectrum of visible light.

In this embodiment, the dispersed dye in each coating has a color or color transfer value corresponding to the complement of the color to which the coating on the particular receptor sheet is sensitized, i.e., a color represented by the combination of ranges of light reflected by the sensitized photoconductor.

By way of illustration, the visible spectrum may be divided into contiguous segments, preferably three or more segments, such as division of the visible light range of 400 to 700 nm. into segments of approximately 400 to 500 nm., 500 to 600 nm. and 600 to 700' nm. The sensitizing dye for the coating on one of the receptors is selected to sensitize the photoconductor to light within the range of 400 to 500 nm. (blue sensitivity) and to reflect light within the range of 500 to 700 nm. This effect can be achieved by the use of a dyestut't' corresponding to the yellow layer in the well-known photographic color processes based upon the subtractive tripack, such as Auramine (Cl. 41,000) from the Allied Chemical Corporation or Euchrysine GGA from GAF Corporation. The dispersed dye component formulated into the coating on this receptor is a dyestutf having a yellow color or a color which represents the combination of reflected light within the range of 500 to 700 nm.

Another or second receptor is provided with a coating formulated with a sensitizing dye effective to sensitize the photoconductor in the light range of 500-600 nm. (green sensitivity), while reflecting light within the range of 400-500 nm. and 600-700 nm. This can be achieved by the use of a magenta coating, when reference is made to the subtractive tri-pack such as by formulating the coating composition to contain acridine red (C.I. 45,000) from Allied Chemical Corp. or Ethyl Red #2155 from Eastman Organic Chemicals. The soluble dye component formulated into the described coating would be selected of a dyestuif having preferably a blue-red color corresponding to the combination of the reflected light within the range of 400-500 and 600-700 nm.

The third receptor is provided with a coating formulated to contain a sensitizing component which sensitizes the photoconductor to absorbed light within the range of 600-700 nm. (red sensitivity), while reflecting light within the range of 400-600 nm. This can be achieved by a cyan coat, such as with Patent Blue (Cl. 42,045) or a 3-ethyl-2-[5-(3-ethyl-2-benzothiazolinylidene)-1,3- pentadienyl]benzothiazolium iodide, hereinafter referred to as EEBI, from Aldrich Chemical Co. The soluble dye component in the third coating would be selected of a dyestutf giving a blue-green color corresponding to the range of reflected light or the combination of colors within the range of 400-600 nm.

As the photoconductor component of the photoconductive coating, use is preferably made of photoconductive zinc oxide, such as Photox 80 marketed by the New Jersey Zinc Company. However, any of a number of other photoconductors known to those skilled in the art, such as the photoconductors described in US. Patent No. 3,218,318 to Middleton, may also be used.

Similarly, a number of insulating binders are known to the art for use in hotoconductive compositions of the type described, and can be used in accordance with the invention. Representative of such binders are organosilicon resins, butadiene-styrene copolymers, modified alkyd resin (e.g., styrenated alkyd resins), acrylic resins, etc.

When based on the amount of hotoconductive zinc oxide, the photoconductive coating used in accordance with the process of the present invention are preferably formulated to contain the components in the following proportions:

Parts by weight Photoconductor 100.0 Binder -2000 Sensitizer 0001-50 Dispersed dye 0.5-20.0

The foregoing proportions are not critical, and are in part dictated by cost factors. For example, the sensitizer component or components can be employed in quantities greater than 5.0 parts by weight per 100 parts by Weight of photoconductor, although the costs involved become significant when greater amounts are employed.

The coating is preferably applied in the form of a composition containing the foregoing components in combination with an inert diluent which is a solvent for the resinous binder. Application of the composition is generally made in amounts sutficient to provide a dry coating in a coating weight within the range of 5 to 40 pounds per 3,000 square feet of surface area.

Having described the basic concepts of the invention from the standpoint of the compositions used in forming each of the receptors employed in the practice of the invention, reference is now made to the following examples, which are provided by way of illustration and not of limitation, of the practice of the invention in the production of true color copies from a multi-color original. The description will be hereinafter made with respect to a system of three receptor sheets, each of which is sensitized to one of the primary additive colors or red, blue, and green; however, it will be understood that the spectrum of visible light can be otherwise divided for the selection of a sensitizing component and corresponding dispersed dye embodied in the coating on each of the receptor coatings with the number of receptors employed corresponding to the number of divisions in the spectrum of visible light.

EXAMPLE 1 Magenta Coating Composition (Green sensitive) Photoconductive zinc oxide (Photox 'g 100.0 Modified acrylic resin (50% solids in toluene) (DeSoto resin E-202) g 80.0 Dispersed dye Azosol Fast Brilliant Red B-N) g 5.0 Green sensitizing dye (Ethyl Red #2155) g 0.05 Solvent (toluene) ml 250 EXAMPLE 2.

Yellow Coating Composition (Blue sensitive) Photoconductive zinc oxide (Photox 80) g |100.0 Modified acrylic resin (50% solids in toluene- (DeSoto resin E-202) g 80.0 Blue sensitizing (Euchrysine GAA) g 0.5 Dispersed dye (Calcofast Spirit Yellow TG) g 5.0 Solvent (toluene) ml 250 EXAMPLE 3 Cyan Coating Composition (Red sensitive) Photoconductive zinc oxide (Photox 80) g 100.0 Modified acrylic resin (50% solids in toluene) (DeSoto resin E-202) g 80.0 Red sensitizing dye (EEBI) g 0.025 Dispersed dye (Calcofast Spirit Blue TI-IN) g 5.0 1 Solvent (toluene) 250 In forming each of the foregoing compositions, the resinous hinder, the zinc oxide and solvent are first blended to obtain a uniform mixture. The sensitizing dye is added and mixed, and finally the dispersed dye is added and mixed.

Each of the foregoing compositions is then applied to three suitable conductive base sheets, such as Domtar 45-pound b.w. Electrofax paper, in the desired coating weight (15 to 17 pounds per 3000 square feet of surface area). Application of the compositions can be made by use of a roller coater, a metering rod or by hand draw-down with a wire wound rod, and dried. The resulting receptor comprises the base sheet 10 having a substantially uniform photoconductive coating 20 on the face thereof.

Each of the receptor sheets having one of the coatings from Examples 1 to 3 is then charged as by subjecting the face of each receptor sheet to a corona spray as it is exposed to a corona discharge from wires operating at a potential of about 6000 to 8000 volts. The charged wires, which extend over the face of each receptor sheet, are either transported over the face of the receptor sheets, or the receptor sheets are displaced beneath the wires, to thereby deposit a blanket electrostatic charge on each of the sheets.

Each of the charged sheets is then exposed to light modified by an image, such as by projection of a photographic image of the same original. By way of illustration, each of the receptor sheets having photoconductive coatings of Examples 1 to 3, coatings 21, 22, and 23, respectively, are exposed to a multi-color original formed of a blue A, a green B, and a red D, all of which are underscored by a solid black line, on a white background.

With respect to the receptor sheet having the photoconductive coating 21 containing the composition of Example 1, the portion of the original which is green in color (the letter B), cause a corresponding portion of photoconductive coating 21 to be discharged since the photoconductor of coating 21 is sensitized to green. By the same token, areas of coating 21 corresponding to the portions of the original which are blue and red and black in color as represented by the letters A and D and the black line respectively retain an electrostatic charge for subsequent development as shown in FIG. 2 of the-drawing on the magenta coating 21.

As shown in FIG. 3 of the drawing, the photoconductive coating 22 which is sensitized to blue light retains an electrostatic charge on the yellow coating in areas corresponding to the areas of the original which are green, red, and black in color as represented by the letters B and D and the black line, respectively, while the portion of the coating corresponding to the portion of the original which is blue in color as represented by the letter A is discharged.

Similarly, as shown in FIG. 4 of the drawing, the photoconductive coating 23 which is sensitized to red light retains an electrostatic charge on the cyan coating in areas corresponding to the areas of the original which are blue, green, and black in color as represented by the letters A and B and the black line, respectively, while the portion of the cyan coating corresponding to the portions of the original which are red in color as repre sented by the letter D are discharged.

As will be appreciated by those skilled in the art, the white background of the original which includes a combination of green, blue, and red light cause the corresponding areas of each of the coatings on the three receptor sheets to be discharged.

The exposed receptor sheets are then each developed in a conventional manner, using either a dry powder developer or a liquid developer of the type described in copending application, Ser. No. 836,415, filed June 25, 1969, now U.S. Pat. No. 3,630,729. As described in this copending application, use is made of a developer composition in which the conventional toner particles have been replaced by finely divided particles of a material which, when heated to an activated or molten state, is a solvent for the dispersed dye in the photoconductive coating.

Illustrative of liquid developing compositions which can be used in the practice of this invention include the following:

EXAMPLE 4 Developer Composition Toner (antipyrine) g 5.0 Liquid carrier (Isopar G) ml 400.0 Charge director (Fuel oil additive #2) g 5.0

EXAMPLE 5 Developer Composition Toner (l-allyl-2-thiourea) g 5.0 Liquid carrier (Isopar G) ml 400.0 Charge director g 5.0

The liquid carrier used in the above developer compositions is Isopar G from Humble Oil and Refining Co., and is an aliphatic hydrocarbon solvent having a flash point of 104 F. In general, as the liquid carrier, use should be made of aliphatic hydrocarbon solvents in which the toner particles are insoluble.

The charge director, Fuel Oil Additive #2 from Du Pont, is a solution of a methylmethacrylate copolymer having an average molecular Weight of about 50,000 in kerosene. As will be apparent to those skilled in the art, any of a variety of conventional charge directors may be used.

The antipyrine of Example 4 and the l-allyl-2-thiourea of Example 5 are merely representative of suitable toner particles which may be used for development of the latent electrostatic image remaining on the receptor face after exposure. Other toner' particles may be used which meet the requirements:

(1) a solvent for the soluble dye component in the coatings when the toner is in an activated or molten state;

(2) capable of being reduced to a finely divided form in which it is retained in the liquid or powdered developer composition;

(3) capable of taking on a charge,

(4) suitably located within the triboelectric series to produce the desirable charge development.

Representative of other suitable compounds which meet these requirements and can be used as toners are vanillin, 1,6-hexanediol, 1,10-decanediol, ammonium acetate, ethyl urea, acetamide, benzohydrol, 2,2-dimethyl-l, 3-propanediol, ammonium formate and pyrazine. The toner particles can be employed in various concentrations in the developer composition, such as within the rang of 220% by weight, and preferably 3-10% by weight, in a dry powder developer and within the range of 02-20% by weight and preferably 2-10% by weight in a liquid developer. When use is made of a dry powdered developer which is applied by brushing or the like, toner concentration can range up to percent by weight toner in the developer.

Continuing with the development process, in response to the application of the developer composition, toner particles 16 are retained on the portions of the photoconducting coatings of each receptor which remain charged to define a latent electrostatic image after exposure of each receptor, while the discharged portions of the face of each coating remain substantially free of toner particles as schematically illustrated in FIG. 5 of the drawing.

Thereafter, each of the developed receptor sheets is pressed into surface contact with a single copy sheet 30,

as by passage of each developed receptor sheet in contact with the copy sheet 30 between compression rollers heated to a temperature above the melting point of the toner particles, such as a temperature above 111 to 113 C. which is the melting point for antipyrine or a temperature above 77 to 78 C. which is the melting point for l-allyl-Z-thiourea. In general, it is preferred to heat the toner particles to a temperature which slightly exceeds their melting point, such as a temperature 5 to 10 C. above the melting point. As a result, the toner particles are reduced to a fluid state to cause dissolution of the dispersed dye in the underlying portions of each coating in the face of the receptors for transfer of the dye color, as by diffusion, from each receptor to the copy sheet 30.

In the example illustrated in FIGS. 2 to 4, the transfer step described above with the receptor sheet having developed coating 21 on the face thereof results in the formation of a magenta image defining the letters A and D and the line. Similarly, transfer of the dye color from developed coating 22 results in the formation of a yellow image on the copy sheet defining the letters -B and D and the line, and transfer of the dye color from developed coating 23 results in the formation of a cyan image defining the letters A and B and the line.

The cyan and magenta images defining the letter A are superimposed whereby the cyan and magenta colors are mixed to thereby form a blue image defining an A. Similarly, the yellow and cyan color are mixed to define a green B, the magenta and yellow colors are mixed to form a red D, and all the colors are mixed to form the black line. The resulting copy sheet is shown in FIG. 7 of the drawing. As will be appreciated by those skilled in the art, it is important that precise registry of each developed receptor with respect to the copy sheet be maintained during transfer of the dye colors to insure that the developed image A on the cyan coating is coincident with the developed image A on the magenta coating so that the two colors will be mixed on the copy sheet. The same considerations are likewise applicable to the other letters and the line as described.

It will be apparent that the copy produced by the combination of colors from each developed receptor transferred therefrom corresponds to the colored original. The receptor sheets can be used to produce additional copies by successive passage of copy sheets into pressure contact with each receptor sheet until the dispersed dye in the coating on each receptor is exhausted.

In accordance with another embodiment of the present invention, each of the two and preferably three or more receptor sheets is provided with a dispersed dye having a subtractive color with the color or the combination of the dispersed dyes on each of the sheets being black as represented by the same dispersed dyes of the subtractive colors of cyan, magenta, and yellow, as described above, with the sensitizing component being a sensitizer which sensitizes the photoconductor panchromatically, that is over substantially the entire spectrum of visible light. Thus, each of the receptor sheets is exposed to an original using filtered light of a color which is complementary to the color of the dispersed dye in each of the coatings on the receptors. As used herein, reference to the use of filtered light is intended to mean and include the use of filtered light and the use of white light with a filtered original, since such exposure techniques are fully equivalent.

As the panchromatic sensitizing component, use is preferably made of a combination of sensitizing dyes, each of which sensitize the photoconductor to a separate portion of the visible spectrum. Taken together, the combination of all the dyes has the net eilect of sensitizing the photoconductor component over the spectrum of visible light.

In formulating such combinations of sensitizing dyes to panchromatically sensitize the photoconductor component, use is made of at least two sensitizing dyes, and preferably three sensitizing dyes. By way of illustration, it is possible to employ a combination of three sensitizing dyes, each of which sensitize the photoconductor to one of the three primary additive colors of red, green, and blue. Thus, to provide red sensitivity, use should be made of a sensitizing dye which sensitizes the photoconductor to absorbed light within the range of about 600 to 700 nm., such as Patent Blue (CI. 42045) or 3-ethyl-2-[5- (3-ethyl-2-benzothiazolinylidene) 1,3 pentadienyl1- benzothiazolium iodide (EEBI) described above.

To provide the desired blue sensitivity, use should be made of a sensitizing dye which sensitizes the photocon' ductor to absorbed light within the range of about 400 to 500 nm., such as Euchrysine GGA or Auramine described above.

To provide the desired green sensitivity, use should be made of a sensitizing dye which sensitizes the photoconductor to absorbed light within the range of about 500 to 600 nm., such as Ethyl Red #2155 or Acridine Red (CI. 45000) described above.

Thus, considering the visible spectrum to include light within the range of 400 to 700 nm., the combination of one of each of the foregoing sensitizers has the effect of sensitizing the photoconductor to the entire spectrum of visible light.

Having described the concepts of this embodiment of the invention, reference is now made to the following examples of coating compositions which are provided by way of illustration and not by way of limitation of the practice of the invention in producing true color copies from multi-color originals.

EXAMPLE 6 Magenta Coating Composition (Panchromatically sensitive) Photoconductive zinc oxide (Photox g 100.0 Modified acrylic resin (DeSoto resin 13-202) g 100.0 Green sensitizing dye (Ethyl Red #2155) g 0.05 Blue sensitizing dye (Euchrysine GGA) g 0.25 Red sensitizing dye (EEBI) g 0.07 Dispersed dye (Azosol Fast Brilliant Red Bn) g 5.0 Solvent (toluene) ml 250 EXAMPLE 7 Yellow Coating Composition (Panchromatically sensitive) Photoconductive zinc oxide (Photox 80) g 100.0 Modified acrylic resin (DeSoto Resin e-202) g 0.05 Green sensitizing dye (Ethyl Red #2155) g 0.05 Blue sensitizing dye (Euchrysine GGA) g 0.25 Red sensitizing dye (EEBI) g 0.07 Dispersed dye (Calcofast Spirit Yellow TG) g 5.0 Solvent (toluene) ml 250 EXAMPLE 8 Cyan Coating Composition (Panchromatically sensitive) Photoconductive zinc oxide (Photox 80) g 100.0

Modified acrylic resin (DeSoto resin E-202) g 100.0

Green sensitizing dye (Ethyl Red #2155) g 0.05 Blue sensitizing dye (Euchrysine GGA) g. 0.25 Red sensitizing dye (EEBI) 0.07 Dispersed dye (Calcofast Spirit Blue THN) g 5.0 Solvent (toluene) ml 250 Each of the foregoing coating compositions are applied to a suitable base sheet in the manner described above to form a photoconductive coating on the face of each receptor and d ried. Referring to FIGS. 2 to 4, the coating of the composition of Example 6 is applied to form coating 21, Example 7 to form coating 22 and Example 8 to form coating 23. Thereafter, each of the receptors is charged in the manner described above.

Each of the charged receptors is then exposed to an original, such as a multi-color original using filtered light having a color which is complementary to the color of the dispersed dye in the coating of the particular re ceptor exposed. By way of illustration, three receptor sheets each of which have a photoconductive coating formed from the compositions of Examples 6 to 8 are exposed to the original described above formed of a blue A, a green B and a red D, all of which are under scored by a black line.

Thus, the receptor having the magenta coating 21 of Example 6 is exposed to the original using green light whereby the areas of coating 21 corresponding to the blue, red and black portions of the original as represented by the letters A and D and the black line, respec tively, retain an electrostatic charge while the portion of the coating 21 corresponding to the green portion of the original as represented by the green B is discharged.

Similarly, the receptor having the yellow coating 22 of Example 7 is exposed to an original using blue light to thereby form an electrostatic image corresponding to the green, red and black portions of the original as represented by the letters B and D and the black line respec' tively, while the portion of the coating 22 corresponding to the blue color of the original is discharged.

The receptor having the cyan coating 23 of Example 8 is exposed to the original using red light to thereby form the latent electrostatic images defining the letters A and B and the black line.

Each of the exposed receptors is then developed in the manner described above, and the dye color from each of the coatings is transferred to a copy sheet in the manner described.

It will be apparent that various changes and modifica tions can be made in the details of formulation, procedure and use without departing from the spirit of the invention, especially as defined in the following claims.

We claim:

1. An electrophotographic process for the production of true color copies comprising the steps of applying an electrostatic charge to each of two or more receptors formed of a substrate having a photoconductive coating comprising a binder, a photoconductor, a sensitizing dye and a dispersed'dye, in which the sensitizing dye in the coating on each receptor sensitizes the photoconductor to a particular segment of the spectrum of visible light for absorption of light within that segment and reflection of light outside that segment and in which the dispersed dye in the coating on each receptor has a color corresponding to the light reflected, with the number of receptors corresponding to the number of segments of the spectrum of visible light whereby all of the receptors together are sensitized to substantially the entire spectrum of light, exposing of the receptors to an original whereby areas on the coating of each receptor are discharged in response to color in the corresponding areas of the original to which the coating has been sensitized, leaving an electrostatic charge on the coating of each receptor from which light is reflected, developing each of the exposed receptors with a developer containing a toner which is a solvent for the dispersed dye in response to activation whereby the toner is retained on the coating of each receptor retaining an electrostatic charge, and bringing a copy sheet into surface contact with each of the developed receptors with the toner in an activated state to cause transfer of the dispersed dye color from the corresponding areas of the receptors to the copy sheet.

2. A process as defined in claim 1 wherein the photoconductor is zinc oxide.

3. A process as defined in claim 1 wherein the photoconductive coating is present in a coating Weight of -40 pounds per 3,000 square feet of surface area.

4. A process as defined in claim 1 wherein the coating contains 10-200 parts by weight binder per 100 parts by weight photoconductor.

5. A process as defined in claim 1 wherein the coating contains 0.001 to 5.0 parts by weight of the sensitizer per 100 parts by weight photoconductor.

6. A process as defined in claim 1 wherein the coating contains 0.5 to 200 parts by weight of the dispersed dye per 100 parts of photoconductor.

7. A process as defined in claim 1 wherein the toner is selected from the group consisting of antipyrine and 1-a1lyl-2-thiourea.

8. A process as defined in claim 1 wherein the dispersed dye is a spirit-soluble dye.

9. A process as defined in claim 1 which includes three receptors, each of which contain a photoconductive coating which is sensitized to one of the three additive primary colors of red, blue, and green.

10. A process as defined in claim 1 which includes the step of transferring the dye color from areas of each receptor retaining toner by heating each of the developed receptors to a temperature above the melting point of the toner while the copy sheet is in surface contact with each receptor.

11. A process as defined in claim 1 wherein the dispersed dye in each coating has a color of one of the three primary subtractive colors of magenta, cyan, and yellow.

12. An electrophotographic process for the production of true color copies comprising the steps of applying an electrostatic charge to each of two or more receptors formed of a substrate having a photoconductive coating comprising a binder, a photoconductor, a sensitizing component which sensitizes the photoconductor over substantially the entire spectrum of visible light and a dispersed dye, with the color of the dispersed dye in each of the coatings when combined with the color of the dispersed dye in the other coatings forms substantially black, exposing each of the receptors to an original using light having a color which is complementary to the color of the dispersed dye in the coating of the receptor whereby areas of each coating corresponding to areas of the original having the color light employed is discharged leaving an electrostatic charge corresponding to the areas of the original having a color substantially the same as the light employed, developing each of the exposed receptors with a developer containing a toner which is a solvent for the dispersed dye in response to activation whereby the toner is retained on the coating of each receptor retaining an electrostatic charge, and bringing a copy sheet into surface contact with each of the developed receptors with the toner in an activated state to cause transfer of the dispersed dye color from the corresponding areas of the receptors to the copy sheet.

13. A process as defined in claim 12 wherein the photoconductor is zinc oxide.

14. A process as defined in claim 12 wherein the photoconductive coating is present in a coating weight of 5-40 pounds per 3,000 square feet of surface area.

15. A process as defined in claim 12 wherein the coating contains 10-200 parts by weight binder per parts by weight photoconductor.

16. A process as defined in claim 12 wherein the coating contains 0.001 to 5.0 parts by weight of the sensitizer per 100 parts by weight photoconductor.

17. A process as defined in claim 12 wherein the coating contains 0.5 to 20.0 parts by weight of the dispersed dye per 100 parts of photoconductor.

18. A process as defined in claim 12 wherein the toner is selected from the group consisting of antipyrine and 1-a1lyl-2-thiourea.

19. A process as defined in claim 12 wherein the dispersed dye is a spirit-soluble dye.

20. A process as defined in claim 12 which includes the step of transferring the dye color from areas of each receptor retaining toner by heating each of the developed receptors to a temperature above the melting point of the toner while the copy sheet is in surface contact with each receptor.

21. A process as defined in claim 12 wherein the dispersed dye in each coating has a color of one of the three primary subtractive colors of magenta, cyan, and yellow.

References Cited UNITED STATES PATENTS 2,986,466 5 1961 Kaprelian 961 3,060,020 10/ 1962 Greig 961 3,630,729 12/1971 Bach et a1. 961.2

GEORGE F. LESMES, Primary Examiner M. B. WITTENBERG, Assistant Examiner U.S. Cl. X.R. 96-1.7; 11717.5; 25262.1

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,728, 112 Dated April 17, 1973 In fl Leg H, Qhapin and Robert Egeed l V It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 56, delete "2,290,674" and insert therefor Column 8, line 34, change 'e-202" to 12-202 delete "0,05" and insert therefor 100.0

Signed and sealed this 1st day of January 1974.

Attest: e

EDWARD I I.FLETCHER,JR. RENE D.- TEGTMEYER Attesting Off-ricer Acting Commissionerof Patent-s 

